Knee arthroplasty, and particularly the surgical undertaking of a total knee replacement is generally a complex procedure, which substitutes prosthetic structures for the normal or natural geometry of the articulation surfaces, and frequently must accommodate prior damage to one or more ligaments, bones or tissue structures of the joint, and biological changes or distortions which have evolved therefrom. In general, it is necessary to perform soft tissue balancing and numerous specially aligned cuts at the bone ends in order to install the prosthetic components with correct spacing, alignment and tensioning to prevent improper kinematics from arising as the joint rotates in use, and to avoid the occurrence of accelerated wear patterns or possible joint dislocation. Typically, this requires a number of measurement steps and cutting or fitting steps, often with additional small adjustment cuts to achieve final bone preparation for mounting the metallic and other components of the prosthetic joint. Preliminary soft tissue balancing may be accomplished when the gaps at the bone ends are formed in extension and flexion, for receiving the prosthetic endings. Thereafter, various additional fitting steps may be required to achieve proper patella tracking, and additional soft tissue balancing or adjustment may be required for the patellar tendon, i.e. the quadriceps tendon and the patellar ligament, which together surround and extend from the patella at its upper and lower ends respectively.
Soft tissue tensioning, e.g. surgical relief of the medial and lateral and collateral ligaments and of the patellar tendon, is generally performed by feel, with the surgeon sensing the tension exerted by the relevant soft tissue structure as the major bones are moved through various positions relative to each other. Such tensioning is necessary because tendons and ligaments are relatively inextensible, and the provision of a new joint geometry defined by the prosthetic components may result in the build-up of extreme tensile forces or excessive looseness in one or more positions, as well as lateral forces due to the displacement of one or more surfaces or axes of the prosthesis from those of the natural joint or previous prosthesis it replaces.
It would therefore be desirable to provide a tool to more effectively determine the tensile forces of the relevant tissue, and to conveniently assess tension at various stages of the procedure, both for identifying initial values, and for subsequently correcting changes in the tensile loading occasioned by the new joint geometry of the prosthesis.